Simulating Cat Dynamics
This article is for one special kitty who was there for me during the first few years of my VFX journey.
Fun Facts About Cats
We love our furry friends because they are purrrr-fect. (Ok I’ll stop…). But they have some awesome physical attributes that we just can’t compare to.
Out of all the cats in the world, there is only one species of them that are domesticated. The rest are wild. This species is called Felis catus. From this species there are 60 different registered breeds of our furry friends.
Most cats contain the following features: A strong flexible body, quick reflexes, sharp teeth and retractable claws, night vision, a well developed sense of smell, and some form of communication skill. Depending on your own cat, the range of the communication will vary. They are mostly active between dusk and dawn, and hunt small mammals. However, they are so efficient in their killings that they contribute to the extinction of various bird, mammal, and reptile species.
It is thought that the first domesticated cats were African wild cats that were tamed between 7500–7200 BC in southern Cyprus. It is thought that the wildcats were attracted to the large amount of rodents that would live in human cities, and decided to live around the settlements. However, development of selective cat breeds wouldn’t start till the 19th century.
In the wild, there are currently 40 known species of wildcats. These include the African Wild Cat, Tigers, Lions, Ocelots, and Clouded Leopards.
Cats have amazing eyesight. They have a visual field of 200 degrees. Which is about 20 degrees more than humans. Peripheral for cats is also much wider. They have about 30 extra degrees of vision.
Cats were also thought to only see two colors. White and black. Just like dogs. However their sight spectrum reaches into the blue-violet and green-yellow color areas.
Humans have many more cones in our eyes than cats. While cats have more rods than us. Rods are the cells in your eyes that allow us to see in the dark, and cones are the cells that allow us to see colors, and sharpness of objects. The high quantity of rods in a cat’s eyes allow for it to sense motion faster and follow fast moving objects.
All cats have at least four categories of hair or fur. The different types are layers on top of each other and serve different purposes.
Guard Fur: This is the outermost layer of fur on a cat. It is the layer of fur you see on the surface of the animal. It does contain too much of the color patterning in the creature, but instead guards it from the cold, and water. The guard fur is the longest fur layer on a cat’s body. It is also more coarse than the other fur and hair groups.
Down Fur: This fur is the cat’s insulation layer. The thickness of the fur is dependent on where the cat is living and what breed it is. For example, if a cat is a Maine Coon it will have a very large insulation layer, and even more so if it is living in a cold environment. This is the fur that your cat leaves on your carpet everyday.
Awn Fur: This fur glues the down and guard fur together. This fur is longer and thinner than the Down Fur, but shorter and thicker than Guard Fur. This fur contains the color patterns of your cat.
Whiskers: These are hairs on your cat made of keratin. They serve a lot of functions on a cat and are attached to nerves on the cat's face. They allow a cat to decide if they can fit in a space, and orient them in their environment.
Depending on the type of cat, your cat can have different styles, and types of fur.
Long Fur: Long fur will only develop on certain breeds of cats. It will grow between 1.5-5 inches long.
Crimped Fur: This is fur that looks partially wavy. It is usually seen in kittens, and in specific breeds of cats. Such as the Cornish Rex, Devon Rex and Selkirk Rex.
Short Fur: Short haired cats are the most common type of cat. The fur doesn’t grow beyond 1.5inches.
Hairless: A hairless cat is not actually hairless, but rather they are extremely short haired. They feel very velvety, and soft. However, because of their very short hair, they cannot soak up natural oils from the cat’s skin or other contaminants that fall on the cat’s body.
Cat’s also have several different color patterns on their coats.
Solid Coats: A solid coat is a single colored cat. Solid colored cats are not that common.
Bi-Color Coats: Bi-Colored cats are cats with two different colors. Depending on where the colors are located on the cat, the pattern can have different names, For example, a randomly spotted black and white cat can be called a magpie colored cat.
Tabby Coats: Tabby fur is the most common type of fur seen in cats. This coloring is seen around many crossbred breeds. This fur has either a striped or marble look. It can also have vertical stripes, dots, and marble patterns.
Calico Coats: This fur type contains three different colors. It can be orange, black, white, or brown.
Tortoiseshell Coats: This pattern is similar to a calico pattern. The patterns can blend together and look very fractal-like. It can contain orange, black, white, and brown colors.
Torbie Coats: This fur coat is a mix of a tabby and tortoiseshell cat hair.
Color Point Coats: These fur coats are mostly made up of one color, but will add a secondary color on the cats face, nose, paws, and tail. So there are color points on each end of the cat.
Cat Skeletal Systems
Cat skeletons are very different from humans. To start, cats have seven cervical vertebrae, meaning they have less bones in their necks than humans, but just as much as the average mammal. Attached to a cat’s spine are 13 ribs, the shoulders, and the pelvis.
A cat’s skull is unusually shaped, as it is more oval in appearance than other skulls. They have very large eye sockets, and jaws full of canine teeth. These teeth are narrowly spaced in their jaws for more ease when it comes to killing small rodents.
Cats' claws are also a key part of their skeleton. They are protractable and retractable. Around the claws are the fur and skin of the cat’s toe pads. This keeps the claws sharp and protects them from friction with the ground as they walk. Cat’s shead the outer layer of their claws when scratching surfaces.
Cat simulations are used all over the world. Mostly because they are one of the most popular pets on earth, and are very efficient in nature.
In the computer world, IBM and Stanford University have studied cats to model their brains. In 2009, they were able to simulate a cat’s cerebral cortex using their Blue Gene/IP Supercomputer. In 2007, they had also done the same with a rat’s brain. As well as 1% of the human brain in 2009.
The simulated cat brain runs 100 slower than a real one, but allows researchers to visualize the connections and the cortical behaviors better than studying the real thing. The whole cortex simulation is meant to mimk 1 billion brain cells and 10 trillion learning synapses with its communication connections. Scientists hope to simulate the human brain within the next 10 years.
Meanwhile over at Google, they are also studying neural networks. However, they are using over 16,00 thousand computer processors to identify cats on the internet. This system is one of the largest neural computer networks in the world. But it’s first task was to identify what makes up our furry felines.
However, they didn’t ask this network to specifically look for cats. They first showed the system a collection of 10 million digital images, and allowed it to choose what it wanted to look for. So the network taught itself to recognize cats amongst thousands of other objects.
These systems are trying to help computer scientists program machine vision and perception, speech recognition and language translation into AI. Even if it is something as simple as looking for a cat.
Some veterinary universities are also creating virtual cat projects to understand how cats respond under anesthesia and surgeries. Understanding how cats react to new pharmaceutical drugs and sedatives can help vets better prepare an animal for an operation. These simulations can simulate a cat’s blood pressure, heart rate, skeletal muscles, and membranes.
Cats in VFX
We already know that Houdini and other 3D softwares have some amazing hair and fur grooming tools. In Houdini there are many quickstart ways to create hair on an object, and customize it as well. But let’s take a look at some excellent examples from the VFX community.
In the movie Captain Marvel, there was a very friendly alien kitty taking part in a good chunk of the movie. So it was essentially for the VFX team to make a CG cat that would be similar and realistic to the actual cat on set. Their CG cat was so good, that when shown the real and CG cat side by side it confused some Marvel staff on which cat was the real one. Trixer Studios did a very puuuurfect job. HERE.
Cats are also used in game development, and motion capture. DIGIC Services is a 3D animation & Visual effects production company in Budapest. Recently, they created a reel of some motion capture they did with some talented stunt cats. I highly recommend watching it: HERE.
Another cool kitty is one created by Kristin Farrensteiner. Kristin Farrensteiner a groom artist at industrial Light and Magic. She and The Gnomon Workshop teamed up to produce a hair and groom series on how to groom a cat. The series is called Creating Creature Hair & Fur Grooms in Houdini. It aims to teach others how to create a photorealistic cat model in Houdini. She goes over how to simulate the whiskers, face, ear hair, and mesh attributes.
You can check out the workshop: HERE.
What Is the Difference Between Cat Hair and Fur?: https://www.thesprucepets.com/cat-fur-vs-hair-554813
Coat and Skin Appearance in the Healthy Cat: https://vcahospitals.com/know-your-pet/coat-and-skin-appearance-in-the-healthy-cat
Cat coat genetics: https://en.wikipedia.org/wiki/Cat_coat_genetics
15 Different Types of Cat Furs: Colors & Patterns: https://excitedcats.com/different-types-of-cat-furs/
You Can Pet a Virtual Cat and Feel Its Simulated Fur Using This Elaborate VR Controller: https://gizmodo.com/you-can-pet-a-virtual-cat-and-feel-its-simulated-fur-us-1846898198
IBM’s Blue Gene Supercomputer Models a Cat’s Entire Brain: https://www.popsci.com/technology/article/2009-11/digital-cat-brain-runs-blue-gene-supercomputer/
Cat brain-based computer: Scientists perform cat-scale cortical simulations and map the human brain: https://www.sciencedaily.com/releases/2009/11/091118133535.htm
The Cat is Out of the Bag: Cortical Simulations with 109 Neurons, 1013 Synapses: https://people.eecs.berkeley.edu/~demmel/cs267_Spr10/Lectures/RajAnanthanarayanan_SC09-a63.pdf
What Do Cats See?: https://nickolaylamm.com/art-for-clients/what-do-cats-see/
How Many Computers to Identify a Cat? 16,000.: https://www.nytimes.com/2012/06/26/technology/in-a-big-network-of-computers-evidence-of-machine-learning.html
First Full-Scale Simulation of Cat-Size Cortex is a Gordon Bell Prize Winner: https://cs.lbl.gov/news-media/news/news-archive/2009/first-full-scale-simulation-of-cat-size-cortex-is-a-gordon-bell-prize-winner/
The Virtual Cat: http://spider.science.strath.ac.uk/sipbs/software_sims_cat.htm
The evolutionary origins of the cat attractant nepetalactone in catnip: https://advances.sciencemag.org/content/6/20/eaba0721
Estimation of effectiveness of three methods of feral cat population control
by use of a simulation model: https://ase.tufts.edu/biology/labs/reed/documents/pub2013McCarthyFeralCatControl.pdf
Brain Modeling ToolKit: An open source software suite for multiscale modeling of brain circuits: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7728187/
WHAT GOES ON BEHIND THE SCENES WHEN A VFX STUDIO DOES ONE OF THOSE ‘REAL VS. CG’ TEST SHOTS?: https://beforesandafters.com/2019/04/04/what-goes-on-behind-the-scenes-when-a-vfx-studio-does-one-of-those-real-vs-cg-test-shots/
How ‘Captain Marvel’ VFX Team Crafted a Scene-Stealing Cat: https://www.hollywoodreporter.com/movies/movie-news/how-captain-marvel-vfx-team-crafted-a-scene-stealing-cat-1254003/
MOTION CAPTURING CATS. THAT’S IT. THAT’S THE POST.: https://beforesandafters.com/2021/04/13/motion-capturing-cats-thats-it-thats-the-post/
Brenda the Cat: CGi Breakdown: https://www.youtube.com/watch?v=M3YNEUpgKcY
Cat Groom: https://www.artstation.com/artwork/d86oYW
Groom Merge object node: https://www.sidefx.com/docs/houdini/nodes/obj/groommerge.html
Groom Blend geometry node: https://www.sidefx.com/docs/houdini/nodes/sop/groomblend.html
Hair and fur: https://www.sidefx.com/docs/houdini/fur/index.html
Creating and styling fur with guide processes: https://www.sidefx.com/docs/houdini/fur/teddybear.html